Method and means for triboelectric evaluation of a fabric



Dec. 30, 1969 R m 3,487,296

METHOD AND MEANS FOR TRIBOELECTRIC EVALUATION OF A FABRIC Filed Feb. 20. 1968 5 Sheets-Sheet 1 H 2 ie- 4 mm/v0 iyig g um BY AA @m ayt W M ATTORNEYS Dec. 30, B969 E. R; FREDERICK METHOD AND MEANS FOR TRIBOELECTRIC EVALUATION OF A FABRIC Filed Feb. 20, 1968 3 Sheets-Sheet 2 ATTORNEYS Dec. 30, 1969 METHOD AND MEANS FOR 'TRIBOELECTRIC EVALUATION 'OF A FABRIC Filed-Feb. 20, 1968 C5 Sheets-Sheet 3 INVENTOR EDWARD R. FREDERICK ATTORNEYS E. R.. FREDERICK 3,487296 United States Patent 3 487 296 METHOD AND MEANsFoR TRIBOELECTRI'C EVALUATION OF A FABRIC Edward R. Frederick, Pittsburgh, Pa., assignor to Albany Felt Company, Albany, N.Y., a corporation of New York Filed Feb. 20, 1968, Ser. No. 706,905

Int. Cl. G01r /28 U.S. Cl. 324--32 6 Claims ABSTRACT OF THE DISCLOSURE A reproducible tribolectrification and charge evaluation method and means applicable to fiber, fabric and other materials in which a test fabric under tension is brought into rubbing contact with a reference fabric and then the two are separated and the static charge on the test fabric is determined.

BACKGROUND OF THE INVENTION In the manufacture and use of industrial fabrics electrostatic charge evaluation and control are significantly important.

Of particular importance today are the electrostatic properties of synthetic fiber carpeting and upholstery wherein the build-up of high charges can result in discomfort to human beings. Also, belting fabrics are used in areas where fireproofing is important and frequently batteries are used to build up desirable charges and voltages on machines. Also, copying machines frequently depend upon the control of electrostatics as part of their function as do fume :bags. Further, the electrostatic properties of materials are significant due to the electrostatic effect on the build-up of dirt or lint.

While the phenomenon of static electrification is familiar, suitable methods for reproducibly generating and measuring static charges on materials are not available.

When two materials such as fabrics are in contact, electrons can move from one fabric to the other. One of the fabrics then has a deficiency of electrons to provide it with a slight net positive charge. If the two fabrics are good conductors of electricity and are separated, the excess electrons in the one fabric will return to the other before contact is completely broken. However, if one or both of the fabrics is an insulator, the flow of electrons will be impeded and if the separation is accomplished rapidly some of the electrons are trapped in one of the fabrics. Both separated fabrics then remain charged.

Fibers, natural and synthetic, are excellent insulators, especialy when dry. These materials respond to contact electrification and because of molecular differences gain or lose electrons differently. Thus, different fibers display different relative polarities. When listed according to their electropositive or electronegative properties a series can be developed. This series is referred to as the triboelectric series. Any material may be inserted in the series according to its polarity relative to the others in the listing.

Triboelectrification (frictional) by the rubbing process is a reliable method for estimating the relative polarity, intensity, and dissipation rate of electrostatic charges that can be produced on a material. The resulting data are useful if certain important conditions are recognized. That one material develops a higher charge (more positive or more negative) than another does not mean necessarily that it is higher or lower in the triboelectric series than the other. Only if the surface smoothness or roughness of the specimens were exactly the same would this be true. In order to arrive at a reliable location for a given material, it must be rubbed by many fabrics that make up, or are intended to be included in, the series. Only when the test specimen is found to be negative to one and positive to another material, as they are located in adjacent positions in the series, can the specimen be placed between them.

SUMMARY OF THE INVENTION The electrostatic generator and testing means disclosed herein resides in the application of rubbing techniques under controlled conditions to provide reliable and useful electrostatic data on a wide variety of materials.

In practicing the invention, each material to be included in a triboelectric series is utilized both as the rubbed specimen and as the rubbing specimen. Once an indication is obtained as to the relative polarity of the sample, that sample is then used as the rubbed specimen and the rubbing specimen for another material, preferably one located near it in the series. The rubbed material and the rubbing material are located at or near the same relative position in the series if upon rubbing one with another or with a third material no significant charging occurs. A low charge generation or detection can also result if one or both materials is antistatic. If a difference in polarity between samples is found, the sample materials are located in the series relative to one another in accordance with this difference.

Having established a triboelectric series from the evaluation of a variety of different materials suitably representative of the materials per se, any new material may be included in the same series after a few measurements.

DESCRIPTION OF THE DRAWINGS In the accompanying drawings:

FIG. 1 is a plan view of a static generator and evaluator constructed in accordance with this invention in charging position;

FIG. 2 is a plan view of the static generator and evluator of FIG. 1 in measuring position;

FIG. 3 is a transverse sectional view taken along the line 3-3 in the direction of the arrows in FIG. 1;

FIG. 4 is a transverse sectional view taken along the line 4-4 in the direction of the arrows in FIG. 2;

FIG. 5 is a longitudinal Sectional view taken along the line 5-5 in the direction of the arrows in FIG. 1; and

FIG. 6 is a longitudinal sectional view taken along the line 6-6 in the direction of the arrows in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIGS. 1, 3 and 5 the generator and evaluator which is the subject of this invention is shown in charging position. Motor 10 which is the power source and removable voltage proble 11 are supported upon platform 12 which is movable with respect to base 13 to the right and left in FIG. 1 on rod tracks 14 and 15 which are supported upon base 13 by brackets 16 and 17 and which are journalled through the platform 12. The test probe 11 is supported upon the platform 12 by probe support 18 which can hold the probe in fixed position.

Fabric 19 which is to be charged is supported in a rack consisting of rods 20 and 21 maintained in position and supported above the base 13 by end brackets 22 and 23. End brackets 22 and 23 together with rods 20 and 21 comprise the test fabric support frame. Clamp 24 which is attached to the test fabric support frame, as seen best in FIG. 3, holds one end of test fabric 19 in position relative to the frame while the remaining end thereof is engaged by clamp 25 and the fabric is drawn taut by weight 26 which is attached to clamp 25. The weight 26 tensions the test fabric and maintains it across rods 21 and 20.

Support bracket 27 which is mounted upon the base 13 supports a pulley rod 28 over which tensioning string 29 is suspended. One end of the tensioning string 29 is attached at 30 to the test fabric support frame which is pivotally connected at 31 to base 13 and the remaining end of string 29 supports weight 32. Through the force developed weight 32 tends to pivot the test fabric support frame about pivot 31 causing the test fabric 19 to engage the reference fabric covered wheel 33.

Wheel 33 is mounted upon shaft 34 of motor 10 and the circumference of wheel 33 is wrapped with the reference fabric 35. With such an arrangement the tensioning of the test fabric 19 in the test fabric support frame is predetermined and of a fixed amount. At the same time, the weight 32 maintains the test fabric in a predetermined position and with a predetermined force against the reference fabric on wheel 33.

Therefore, in the subject device, in charging the test fabric the reference wheel is positioned as shown in FIGS. 1, 3 and and the motor energized for rotation of the reference wheel rubbing the test fabric by the reference fabric.

After charging, the platform 12 is moved to the right in FIG. 1 and into the position shown in FIGS. 2, 4 and 6 wherein the test probe 11 is in position adjacent the test fabric 19. The reading of the probe at meter 36 is recorded.

The test fabric is then removed and a second fabric placed in position on the test fabric support frame. The platform 12 is returned to the position shown in FIGS. 1, 3 and 5 and the weights fixed in position. The motor is energized and the new test fabric is rubbed by the reference fabric. The tautness of the new test fabric and the force of the test fabric against the reference fabric are substantially the same as in the testing of the first test fabric 19 due to utilization of weights and removal of operator error. The new test fabric is read in the position of FIGS. 2, 4 and 6 and the meter reading recorded. If the meter reading for the new test fabric is close to that of the original test fabric 19 they are placed close together in the series. Additional fabrics are then tested in the same manner and the series developed.

If the meter reading obtained on a new test fabric is low, this sample and the rubbing reference fabric may be relatively close in their location in the triboelectric series; or either fabric may possess conductive or antistatic properties that are manifested by a very high rate of charge dissipation. Even though change generation characteristic of the basic material may take place, the duration of the charge can be extremely short-lived because of an antistatic surface. Antistatic features are specified by high rates of discharge or consistently low readings when a material is rubbed by a variety of clean positive and negative fabrics. Only when the specimen is free of interfering surface finishes, whether intentionally applied or contaminated, can the inherent and true electrostatic properties of the base material be specified. The device, therefore, also permits the detection of conductive or antistatic properties, both natural and as intentionally applied.

As an example of the use of this procedure, two very similar fabrics of staple yarn, Sample A and Sample B, were selected as references. The Sample A, known to be moderately electropositive, was arbitrarily located in a series at +4. The Sample B, known to be moderately electronegative, was arbitrarily located in the same series at -6. Ten units, therefore, separate these two reference materials. Each of these references serves in separate tests as the rubbing material against other fabrics. Sample C, for example, develops a positive charge when rubbed by both materials. It must, therefore, be located above Sample A in the series. In order to specify an exact location for Sample C, it would have to be rubbed by other materials above Sample A until two adjacent materials were found that separately produced positive and negative charging. Sample C, then, must develop a positive charge when rubbed by any material below it in the series and a negative charge when rubbed by any material above it in the series. If no charge develops when it is rubbed by one of the materials and Sample C is not antistatic but some charge is produced by another rubbing fabric, Sample C is located at the same location as the first-mentioned material.

Sample D is then rubbed by Sample A and produces a negative charge of 9 volts (-9 v.) When rubbed by Sample B on the reference wheel, Sample D produces a positive charge, for example, of 21 volts. Since the total difference (21+9) represents 10 units on the arbitrary scale, Sample D is located approximately at below Sample A or at +1(+43). The location as indicated by Sample B rubbing data is also given at +1 by above Sample B or (+76=+1).

Similarly, Sample E is found to develop a negative charge of 6 volts against the Sample A rubbing reference and +4 volts against the Sample B rubbing reference. (Sample E with low charge development could be a smooth multifilament type of fabric, for example.) Likewise, Sample F could produce a negative charge of 32 volts against Sample A and a positive charge of +8 volts against Sample B.

Sample E, although charging to only 4 volts against Sample B, is more positive than Sample F which produces 8 volts against the same reference.

Human errors, variations in spring tensions and handling variations that might be introduced by different operators have been avoided or reduced by the utilization of fixed weights on a sample in a frame and on the test specimen as positioned against the rubbing fabric. A charging position is maintained for the test material when a standard amount of compression against the reference fabric is achieved by causing tension on the test fabric through one of the weights.

Such a procedure can be readily repeated until the evaluation has been completed.

I claim: I

1. An electrostatic generator and evaluator device including in combination a test fabric support frame, a test fabric supported in said test fabric support frame, means for tensioning said test fabric, a reference fabric, means for urging said test fabric and said reference fabric into contact with one another, means for moving said reference fabric and said test fabric relative to one another in rubbing contact, means for separating said test fabric and said reference fabric and probe means for determining the static charge on said test fabric.

2. An electrostatic generator and evaluator device in accordance with claim 1 in which the means for tensioning the test fabric is a clamp constructed and arranged to hold an edge of said test fabric to said frame and a weight of predetermined value attached to remaining edge of said test fabric to develop a force in a direction away from said clamp.

3. An electrostatic generator and evaluator device in accordance with claim 1 in which said test fabric support frame is pivotally mounted and said means for urging said test fabric and said reference fabric into contact is a weight operatively connected to said support frame and developing a force urging said test frame toward said reference fabric.

4. An electrostatic generator and evaluator device in accordance with claim 1 in which the reference fabric is mounted on a wheel as the circumference thereof and the means for moving said reference fabric is a motor drive for said wheel.

5. An electrostatic generator and evaluator device in accordance with claim 4 in which said test fabric support frame is movable relative to said wheel.

6. A method of developing a triboelectric series consisting of providing a first test fabric and a reference fabric, mounting the first test fabric on a pivotal platform, mounting the reference fabric on a movable support, fixing an edge of said first test fabric to said pivotal platform and drawing said first test fabric taut by fixing a weight thereto, attaching a second weight to the pivotal platform to urge said first test fabric against said reference fabric, moving said reference fabric relative to said first test fabric, separating said first test fabric and said reference fabric, measuring the electrostatic charge on said 6 second test fabric and repeating the above steps and positioning said first and second test fabrics in a triboelectric series relative to the difference between the electrostatic charges measured.

References Cited UNITED STATES PATENTS 2,663,842 12/1953 Graham 324-32 2,787,784 4/1957 Meryman et al. 32432 X 10 WILLIAM F. LINDQUIST, Primary Examiner C. F. ROBERTS, Assistant Examiner US. Cl. X.R.

first test fabric, replacing said first test fabric with a sec- 15 3107; 324-72. 

